Minicharged particles (or milli-charged particles) are a proposed type of subatomic particle. They are charged, but with a tiny fraction of the
charge of the electron. They weakly interact with matter. Minicharged particles are not part of the
Standard Model. One proposal to detect them involved photons tunneling through an opaque barrier in the presence of a perpendicular magnetic field, the rationale being that a pair of oppositely charged minicharged particles are produced that curve in opposite directions, and recombine on the other side of the barrier reproducing the photon again.
Minicharged particles would result in vacuum magnetic
dichroism,
and would cause energy loss in
microwave cavities.
Photons from the
cosmic microwave background
In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...
would be dissipated by galactic-scale magnetic fields if minicharged particles existed, so this effect could be observable.
In fact the dimming observed of remote supernovae that was used to support
dark energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
could also be explained by the formation of minicharged particles.
Tests of Coulomb's law can be applied to set bounds on minicharged particles.
References
Hypothetical particles
Dark matter
{{particle-stub